Tensioner with spring force control in a second  bore

ABSTRACT

A tensioner for tensioning a chain span which uses two pistons. The movement of the two pistons may be coupled together. The first piston provides damping to the chain span and a second piston provides variable, dominant and automatically adjusting spring force to the chain span. The tensioner automatically adjusts the mean tension force to keep the chain tension as low as possible without sacrificing chain control, significantly improving drive efficiency at new chain conditions and conditions with dynamic loads.

BACKGROUND OF THE INVENTION

Field of the Invention

The invention pertains to the field of tensioners. More particularly,the invention pertains to a tensioner with spring force control in asecond bore of the housing.

Description of Related Art

Generally, in timing chains for valve drives of internal combustionengines, camshaft chains in use for a camshaft-camshaft drive, andbalancer chains have tensioners that are used on the slack side of achain to take up slack in the chain and to apply tension to the chain.

During operation, a piston of the tensioner presses against the chain tomaintain tension in the chain. When tension in the chain increasesduring operation due to resonance of a chain span, a high load from thechain acts on the piston of the tensioner, causing the piston to extendas the tensioner pumps up to keep the tension in the chain.

Chain drive tensioner spring force is often too high for most operatingconditions because the spring force needs to be sufficient to handleworst case operating conditions of the tensioner system. Theeffectiveness of the tensioner and the overall system behavior andefficiency could be improved if the tensioner spring force could bevaried with operating conditions, taking into account wear andstretching that occurs in the chain during the life of the chain.

SUMMARY OF THE INVENTION

A tensioner for tensioning a chain span which uses two pistons. Themovement of the two pistons may be coupled together. The first pistonprovides damping to the chain span and a second piston provides variableand automatically adjusting spring force to the chain span. Thetensioner automatically adjusts the mean tension force to keep the chaintension as low as possible without sacrificing chain control,significantly improving drive efficiency at new chain conditions andconditions with dynamic loads.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a schematic of a tensioner of a first embodiment of thepresent invention.

FIG. 2a shows a schematic of a tensioner of a second embodimenttensioning a chain under normal operating conditions. FIG. 2b shows aschematic of a tensioner tensioning a chain in response to high dynamicload.

FIG. 3a shows a schematic of a tensioner of a third embodimenttensioning a chain under normal operating conditions. FIG. 3b shows aschematic of a tensioner tensioning a chain in response to high dynamicload.

FIG. 4a shows a schematic of a tensioner of a fourth embodimenttensioning a chain under normal operating conditions. FIG. 4b shows aschematic of a tensioner tensioning a chain in response to high dynamicload.

FIG. 5 shows a schematic of a first piston in a first bore connected toa second piston in a second bore.

FIG. 6 shows a schematic of a second piston in a second bore moving afirst piston in a first bore through an extension of the first piston.

FIG. 7 shows an example of the tensioner of the first embodimenttensioning a chain through an arm.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1-7 show tensioners using a passive control system to maintaintension of a chain span or belt. Passive control is defined as a systemin which no feedback is used to regulate the position of a first pistonrelative to a second piston or between the position of a moveable sleeverelative to the position of a piston.

The tensioner systems of the present invention include a tensioner(described in further detail below) for a closed loop chain drive systemused in an internal combustion engine. It may be utilized on a closedloop power transmission system between a driveshaft and at least onecamshaft or on a balance shaft system between the driveshaft and abalance shaft. The tensioner system may also include an oil pump and beused with fuel pump drives. Additionally, the tensioner system of thepresent invention may also be used with belt drives.

FIG. 1 shows tensioner systems using passive control to maintain theposition of a moveable sleeve 10 relative to a piston 3. Passive controlis defined as a system in which no feedback is used to regulate theposition of a movable sleeve 10 relative to a piston 3 of the tensioner1. The passive system is in contrast to an active control system inwhich real time feedback of components of the engine are used toregulate the position of the movable sleeve 10.

The tensioner 1 includes a housing 2 having a first axially extendingpiston bore 2 a. Received within the bore 2 a of the housing 2 is amoveable sleeve 10. The moveable sleeve 10 has a first open end 13 a anda second open end 14 a which are separated by an inner flange 11 with athrough hole 12. The first open end 13 a is defined by a top innerdiameter portion 13, a top surface 15 of the inner flange 11 and thesecond open end 14 a is defined by a bottom inner diameter portion 14and a bottom surface 16 of the inner flange 11. The through hole 12 ofthe inner flange 11 connects the first open end 13 a with the secondopen end 14 a. A top surface 17 of the moveable sleeve 10 is exposed toatmospheric pressure of the engine.

Received within the first open end 13 a of the moveable sleeve 10,defined by the top inner diameter portion 13 and the top surface 15 ofthe inner flange 11, is a hollow piston 3. Within the hollow piston 3 isa piston spring 4 biasing the piston 3 outwards from the housing 2. Thepiston spring 4 has a first end 4 a in contact with the inner portion 3a of the hollow piston 3 and a second end 4 b in contact with a topsurface 15 of the inner flange 11 of the moveable sleeve 10. It shouldbe noted that while the piston 3 is shown as being hollow, the presentinvention could also apply to a solid piston, with the piston springconnecting the end of the piston.

Received within the second opening 14 a of the moveable sleeve 10,defined by the bottom inner diameter portion 14 and the bottom surface16 of the inner flange 11, is a bias sleeve spring 5. The first end 5 aof the bias sleeve spring 5 is in contact with a bottom surface 16 ofthe inner flange 11 of the moveable sleeve 10 and the second end 5 b ofthe bias sleeve spring 5 is in contact with a check valve 8 of the bore2 a. The bias sleeve spring 5 provides a bias force to maintain someoutward force on the moveable sleeve 10. A pressure chamber 18 is formedbetween the top inner diameter portion 13 of the moveable sleeve 10, thebottom inner diameter portion 14 of the moveable sleeve 10, the bore 2 aof the housing, and the interior 3 a of the piston 3. The through hole12 is present in the inner flange 11 and allows fluid to flow from thesecond opening 14 a to the first opening 13 a of the moveable sleeve 10.

At the bottom of the bore 2 a is an inlet supply line 6 which providesfluid to the pressure chamber 18 through an inlet check valve 8.

At least a portion of the moveable sleeve 10 is coupled to a secondpiston 20 received within a second axially extending piston bore 2 b ofthe housing 2 through a coupling 22. While the second piston 20 is shownas being connected to the top of the moveable sleeve 10, the connectioncan occur on other parts of the moveable sleeve 10. The coupling 22 maybe a sleeve tab as shown in FIG. 1 or a flexible linkage. The secondpiston 20 does not need to be rigid or hard connection to the moveablesleeve 10 and can bias the moveable sleeve 10 from any contact point onthe moveable sleeve 10.

Furthermore, while the second bore 2 b of the housing 2 is shown asbeing parallel to the first bore 2 a, the second bore 2 b may beperpendicular to the first bore 2 a or at some other angle relative tothe first bore 2 a.

In an alternate embodiment, the orientation of the second piston 20could be inverted or reoriented to act on a coupling 22 that then biasesthe moveable sleeve 10, outwards from the housing 2.

In yet another embodiment, the secondary piston 20 could also have aflange around its outer diameter with a chamber on either side as shownin International Application No. PCT/US2012/053830, which is herebyincorporated by reference.

At the bottom of the second bore 2 b is an inlet supply line 9 whichprovides fluid through an inlet check valve 7 to a pressure chamber 24formed between the second piston 20 and the bore 2 b of the housing 2.The coupling 22 between the second piston 20 and the moveable sleeve 10is such that, if the second piston 20 is moved, the moveable sleeve 10moves and vice versa. The fluid from the inlet supply line 9 may also becontrolled by a control valve (not shown).

When the tensioner 1 is tensioning a new chain, during operation, fluidis supplied to the first hydraulic chamber 18 from an inlet supply line6 through an inlet check valve 8 to pressurize the first hydraulicchamber 18 and bias the piston 3 outward from the housing 2 in additionto the spring force from piston spring 4 biasing a span of the closedloop chain.

The supply providing fluid to the first bore 2 a through the first inletsupply line 6 may be the same as the supply providing fluid to secondbore 2 b through inlet supply line 9. Alternatively, the supplysupplying fluid to the first bore 2 a and the second bore 2 b of thehousing 2 can be different.

When the tensioner 1 is tensioning a worn chain without high load,during operation, fluid is supplied to the first hydraulic chamber 18through an inlet check valve 8 from an inlet supply line 6 to pressurizethe first hydraulic chamber 18 and bias the piston 3 outward from thehousing 2. The piston 3 is also biased outward from the housing 2 by thespring 4 to bias a span of the closed loop chain. As the chain wears,the piston 3 has to be biased further outwards from the housing 2 inorder to adequately tension the chain. The bias sleeve spring 5 withinthe second open end 14 a of the moveable sleeve 10 biases the innerflange 11 outward from the housing 2, moving the end 4 b of the spring 4further outwards from the housing 2 and towards the chain.

When the tensioner 1 is tensioning a worn chain during high dynamicchain load, the high dynamic load force from the chain (shown by thearrow) pushes the piston 3 inwards towards the housing 2 and thenoutwards from the housing 2, moving the second piston 20 inwards andoutwards as well, pumping up the pressure or pressurizing the secondpressure chamber 24, by drawing fluid through the inlet check valve 7 inthe second bore 2 b of the housing 2. The pressurization of the secondpressure chamber 24 in the second bore 2 a moves the second piston 20and thus the moveable sleeve 10 outwards from the housing 2. Themovement of the moveable sleeve 10 causes the inner flange 11 of themoveable sleeve 10 to exert an outward force on the piston 3 through thepiston spring 4, opposing the inward force of the dynamic load.

Once the high load is removed from the piston 3, the second pressurechamber 24 is depressurized and fluid leaks out to the engine throughclearance between the second bore 2 b and the second piston 20.

Within the tensioner system of the present invention, movement of themoveable sleeve 10 moves the second end 4 b of the piston spring 4biasing the piston 3 outwards from the housing 2, and therefore thespring force acting on the piston 3 is variable allowing the piston 3 tocontinually tension the chain, even when the chain becomes worn andstretched.

Furthermore, a vent or pressure relief valve (not shown) may be presentwithin the hollow piston 3.

Seals (not shown) may be present between the bore 2 a and the moveablesleeve 10 or any other place within the tensioner as necessary.

Hydraulic stiffness of the tensioner is created by the pressure chambers18 and 24 of the tensioner and substantially prevents inward movement ofthe piston 3 and the moveable sleeve 10 towards the housing 2 when thechain span is under load.

In an alternate embodiment, the moveable sleeve 10 may be receivedwithin another sleeve in the first bore 2 a to aid in eliminatingpressure that could result in undesired pump-up.

It should be noted that this is a mean position control device. It isunlikely that frequency response would be sufficient to dynamically varythe moveable sleeve position within an engine cycle. Pressure acting onthe bottom surfaces of movable sleeve 10 may result in undesiredpump-up. In an alternate embodiment, the moveable sleeve 10 may bereceived within another sleeve in the first bore 2 a to aid ineliminating pressure that could result in undesired pump-up. In anotheralternate embodiment, the piston 3 may fit over the outside of moveablesleeve 10 so the top and bottom surfaces of the moveable sleeve 10 areexposed to the same pressure.

FIGS. 2a-2b shows a tensioner of a second embodiment using passivecontrol to tension a chain under various conditions; FIG. 2a istensioning a chain without high loads; and FIG. 2b is tensioning a chainwith high load.

The tensioner includes a housing 102 having a first axially extendingbore 102 a parallel to a second axially extending bore 102 b. While thesecond bore 102 c of the housing 102 is shown as being parallel to thefirst bore 102 a, the second bore 102 c may be perpendicular to thefirst bore 102 a or at some other angle relative to the first bore 102a.

Slidably received within the first axially extending bore 102 a is afirst piston 103. The first piston 103 has a body with a first end 103a, a second end 103 c, and a hollow interior 103 b. Present within thehollow interior 103 b of the first piston 103 is a first piston spring104. The first piston spring 104 has a first end 104 a in contact withthe interior 103 b of the first piston 103 or a volume reducer 105 and asecond end 104 b in contact with a bottom 102 b of the first axiallyextending bore 102 a of the housing 102. A first pressure chamber 111 isformed between the first piston 103 and the first axially extending bore102 a. Fluid is supplied to the first pressure chamber 111 through afirst supply 106 through an inlet check valve 108. The first piston 103is biased outwards from the housing 102 to bias a chain or belt throughthe first end 103 a of the first piston 103 by the force of the firstpiston spring 104 and the pressure of oil in the first pressure chamber111.

Alternatively, the first piston 103 may not be hollow and the firstpiston spring 104 would contact the body of the first piston 103 and thebottom 102 b of the first axially extending bore 102 a.

The second axially extending bore 102 c receives a moveable sleeve 112.The moveable sleeve 112 has a first open end 112 a and a second open end112 b which are separated by an inner flange 113. The first open end 112a of the moveable sleeve 112 is defined by a top inner diameter portion118 and a top surface 113 a of the inner flange 113. The second open end112 b of the moveable sleeve 112 is defined by a bottom inner diameterportion 119 and a bottom surface 113 b of the inner flange 113. The topsurface 112 d of the moveable sleeve 112 and top surface 113 a of theinner flange is exposed to atmospheric pressure of the engine.

Received within the first open end 112 a of the moveable sleeve 112 is asecond piston 110 having a body with a first end 110 a and a second end110 b. A second piston spring 115 biases the second piston 110 outwardsfrom the first open end 112 a of the moveable sleeve 112 of the housing102 so that the first end 110 a of the second piston 110 can apply aforce to the chain 400, preferably through an arm 401 as shown in FIG.7. The second piston spring 115 has a first end 115 a in contact withthe second end 110 b of the second piston 110 and a second end 115 b incontact with the top surface 113 a of the inner flange 113.

Alternatively, the second piston 110 may be hollow and the first end 110a of the second piston spring would contact a hollow interior of thesecond piston 110.

Received within the second open end 112 b of the moveable sleeve 112 isa bias sleeve spring 116 and an optional volume reducer 114. The firstend 116 a of the bias sleeve spring 116 is in contact with a bottomsurface 113 b of the inner flange 113 or the volume reducer 114 and asecond end 116 b of the bias sleeve spring 116 is in contact with abottom 102 d of the second axially extending bore 102 c of the housing102. The bias sleeve spring 116 maintains the position of the moveablesleeve 112 within the second axially extending bore 102 c and preventsthe moveable sleeve 112 from bottoming out within the second axiallyextending bore 102 c. The bias sleeve spring 116 preloads the secondpiston spring 115, in other words, moving the second end 115 b of thesecond piston spring 115 outwards from the housing 102. A second highpressure chamber 117 is formed between the bottom inner diameter portion119 of the moveable sleeve 112, the bottom surface 113 b of the innerflange 113, and the bottom 102 d of the second axially extending bore102 c. The volume reducer 114 may also be present within this chamber117. There is no fluid communication between the first open end 112 aand the second open end 112 b of the moveable sleeve 112 save for anyleakage that may occur from the second high pressure chamber 117.

Fluid is supplied to the second high pressure chamber 117 through aninlet supply line 109 and preferably a check valve 107. The inlet supply109 may or may not be connected to the inlet supply line 106.

The second piston spring 115 has a greater spring rate or springconstant than the first piston spring 104 or the bias sleeve spring 116.

Since there are two pistons 110, 103 to tension the chain span or belt,the leakage of the first pressure chamber 111 can be increased (asopposed to a conventional hydraulic tensioner where a certain meanpressure must be maintained within the pressure chamber to control thechain) to provide additional damping. The mean force required for chaincontrol is supplied by the second piston 110 in the second axiallyextending bore 102 c.

When the tensioner is tensioning a new chain as shown in FIG. 2a ,during operation, fluid is supplied to the first pressure chamber 111from the first inlet supply 106 and through an inlet check valve 108 andbiases the first piston 103 outwards from the housing 102 in addition tothe spring force of the first piston spring 104, biasing a span of theclosed loop chain 400 or belt as shown in FIG. 7. At the same time, thesecond piston 110 is also biased outwards from the moveable sleeve 112by the second piston spring 115 to bias a span of the closed loop chain400 or belt. Ideally, the first piston 103 and the second piston 110 arebiased outwards from the housing 102 approximately the same amount. Inother words, the first ends 103 a, 110 a of the first and second pistons103, 110 are aligned as shown in FIGS. 2a and 7.

When the tensioner is tensioning a worn chain without high load, duringoperation, fluid is supplied to the first pressure chamber 111 throughthe first inlet supply 106 and through an inlet check valve 108 andbiases the first piston 103 outwards from the housing 102 in addition tothe spring force of the first piston spring 104, biasing a span of theclosed loop chain 400 or belt. At the same time, the second piston 110is also biased outwards from the moveable sleeve 112 by the secondpiston spring 115 due to the movement of the moveable sleeve 112 by thebias sleeve spring 116 to bias the span of the closed loop chain 400 orbelt. As the chain wears, additional slack is present in the chain spanand the first piston 103 and second piston 110 would need to be extendedfurther outwards from the housing 102 to bias and adequately tension thechain 400.

When the tensioner is tensioning a chain during high dynamic chain load,the high dynamic load force from the chain (shown by the arrow) pushesthe first piston 103 and the second piston 110 inwards towards thehousing 102 and then outwards from the housing 102, pumping up thepressure or pressurizing the second pressure chamber 117, by drawingfluid through the inlet check valve 107 into the second bore 102 c ofthe housing 102. The pressurization of the second pressure chamber 117in the second bore 102 c moves the moveable sleeve 112 outwards from thehousing 102. The movement of the moveable sleeve 112 causes the innerflange 113 of the moveable sleeve 112 to exert an outward force on thesecond piston 110 through the second piston spring 115, opposing theinward force of the dynamic load.

Once the inward force of the dynamic load has been opposed, fluid withinthe second pressure chamber 117 leaks to the engine through the secondaxially extending bore 102 c or through the volume reducer 114. Thisleakage reduces the mean pressure present within the second pressurechamber 117.

It should be noted that at all operating conditions, the pressure in thesecond pressure chamber 117 will pump up to maintain a minimum preloadin the second piston spring 115. When the force or preload in the secondpiston spring 115 gets too low, the moveable sleeve 112 moves out fromthe housing, due to the bias sleeve spring 116 and pressure in thesecond pressure chamber 117 and draws more oil in through the inletcheck valve 107.

Therefore, the first piston 103 in the first axially extending bore 102a provides the dominant damping of the chain span 400 or belt and thesecond piston 110 in the second axially extending bore 102 c providesthe dominant and automatically adjusting spring force. The tensioner ofthe present invention automatically adjusts the mean tension force tokeep the chain tension as low as possible without sacrificing chaincontrol, significantly improving drive efficiency at new chainconditions and conditions with dynamic loads.

FIGS. 3a-3b shows a tensioner of a third embodiment using passivecontrol to tension a chain under various conditions; FIG. 3a istensioning a chain without high loads; and FIG. 3b is tensioning a chainwith high load.

The tensioner includes a housing 102 having a first axially extendingbore 102 a parallel to a second axially extending bore 102 c. While thesecond bore 102 c of the housing 102 is shown as being parallel to thefirst bore 102 a, the second bore 102 c may be perpendicular to thefirst bore 102 a or at some other angle relative to the first bore 102a.

Slidably received within the first axially extending bore 102 a is afirst piston 103. The first piston 103 has a body with a first end 103a, a second end 103 c, and a hollow interior 103 b. Present within thehollow interior 103 b of the first piston 103 is a first piston spring104. The first piston spring 104 has a first end 104 a in contact withthe interior 103 b of the first piston 103 or a volume reducer 105 and asecond end 104 b in contact with a bottom 102 b of the first axiallyextending bore 102 a of the housing 102. A first pressure chamber 111 isformed between the first piston 103 and the first axially extending bore102 a. Fluid is supplied to the first pressure chamber through a firstsupply 106 through an inlet check valve 108. The first piston 103 isbiased outwards from the housing 102 to bias the chain through the firstend 103 a of the first piston by the force of the first piston spring104 and the pressure of oil in the first pressure chamber 111.

Alternatively, the first piston 103 may not be hollow and the firstpiston spring 104 would contact the body of the first piston 103 and thebottom 102 b of the first axially extending bore 102 a.

The second axially extending bore 102 c slidably receives a secondexternal piston 150 and a third piston 152. The second external piston150 has a body with a first end 150 a, a second end 150 c, and a hollowinterior 150 b. Present within the hollow interior 150 b is a secondpiston spring 151 for biasing the second piston 150 outwards from thehousing 102. The second piston spring 151 has a first end 151 a incontact with the interior 150 b of the second external piston 150 and asecond end 151 b in contact with a first end 152 a of the third piston152. Alternatively, the second external piston 150 may not be hollow andthe first end 151 a of the second piston spring 151 would contact thebody of the second external piston 150.

The third piston 152 has a body with a first end 152 a, a second end 152c, and a hollow interior 152 b. Present within the hollow interior 152 bis a third piston spring 154 for biasing the third piston 152 outwardsfrom the housing and preloading the second piston spring 151, in otherwords moving the second end 151 b of the second piston spring 152outwards from the housing 102. The third piston spring 154 has a firstend 154 a in contact with the hollow interior 152 b or a volume reducer153 and the second end 154 b is in contact with the bottom 102 c of thesecond axially extending bore 102 c of the housing 102.

A second high pressure chamber 155 is formed between the hollow interior152 b , the second axially extending bore 102 c, and the third pistonspring 154. Fluid is supplied to the second high pressure chamber 155through an inlet supply 109 and preferably a check valve 107. The inletsupply 109 may or may not be connected to the inlet supply line 106.

There is no fluid communication between the hollow interior 150 b of thesecond piston 150 and the second high pressure chamber 155 save for anyleakage that may occur.

The second piston spring 151 has a greater spring rate or springconstant than the first piston spring 104 and the third piston spring154.

Since there are two pistons 150, 103 to tension the chain span or belt,the leakage of the first pressure chamber 111 can be increased (asopposed to a conventional hydraulic tensioner where a certain meanpressure must be maintained within the pressure chamber to control thechain) to provide additional damping. The mean force required for chaincontrol is supplied by the second piston 150 in the second axiallyextending bore 102 c.

When the tensioner is tensioning a new chain as shown in FIG. 3a ,during operation, fluid is supplied to the first pressure chamber 111from the first inlet supply 106 and through an inlet check valve 108 andbiases the first piston 103 outwards from the housing 102 in addition tothe spring force of the first piston spring 104, biasing a span of theclosed loop chain 400 or belt as shown in FIG. 7. At the same time, thesecond piston 150 is also biased outwards from the second axiallyextending bore 102 c by the second piston spring 151 to bias a span ofthe closed loop chain 400 or belt. Ideally, the first piston 103 and thesecond piston 150 are biased outwards from the housing 102 approximatelythe same amount. In other words, the first ends 103 a, 150 a of thefirst and the second pistons 103, 150 are aligned as shown in FIGS. 3aand 7.

When the tensioner is tensioning a worn chain without high load, duringoperation, fluid is supplied to the first pressure chamber 111 throughthe first inlet supply 106 and through an inlet check valve 108 andbiases the first piston 103 outwards from the housing 102 in addition tothe spring force of the first piston spring 104, biasing a span of theclosed loop chain 400 or belt. At the same time, the second piston 150is also biased outwards further through the second piston spring 151 dueto the movement of the third piston 152 by the third piston spring 154to bias the span of the closed loop chain 400 or belt. As the chainwears further, additional slack is present in the chain span and thefirst piston 103 and second piston 150 would need to be extended furtheroutwards from the housing 102 to bias and adequately tension the chain400.

When the tensioner is tensioning a chain during high dynamic chain load,the high dynamic load force from the chain (shown by the arrow) pushesthe first piston 103 and the second piston 150 inwards towards thehousing 102 and then outwards from the housing 102, pumping up thepressure or pressurizing the second pressure chamber 155, by drawingfluid through the inlet check valve 107 into the second bore 102 c ofthe housing 102. The pressurization of the second pressure chamber 155in the second bore 102 c moves the third piston 152 outwards from thehousing 102. The movement of the third piston 152 causes the first end152 a of the third piston 152 to exert an outward force on the secondpiston 150 through the second piston spring 151, opposing the inwardforce of the dynamic load.

Once the inward force of the dynamic load has been opposed, fluid withinthe second pressure chamber 155 leaks to the engine through the secondaxially extending bore 102 c or through the volume reducer 153. Thisleakage reduces the mean pressure present within the second pressurechamber 155.

It should be noted that at all operating conditions, the pressure in thesecond pressure chamber 155 will pump up to maintain a minimum preloadin the second piston spring 151. When the force or preload in the secondpiston spring 151 gets too low, the third piston 152 moves out from thehousing, due to the third piston spring 154 and pressure in the secondpressure chamber 155 and draws more oil in through the inlet check valve107.

Therefore, the first piston 103 in the first axially extending bore 102a provides the dominant damping of the chain span or belt and the secondpiston 150 in the second axially extending bore 102 c provides thedominant and automatically adjusting spring force. The tensioner of thepresent invention automatically adjusts the mean tension force to keepthe chain tension as low as possible without sacrificing chain control,significantly improving drive efficiency at new chain conditions andconditions with dynamic loads.

FIGS. 4a-4b shows a tensioner of a fourth embodiment using passivecontrol to tension a chain under various conditions; FIG. 4a istensioning a chain without high loads; and FIG. 4b is tensioning a chainwith high load.

The tensioner includes a housing 102 having a first axially extendingbore 102 a parallel to a second axially extending bore 102 b. While thesecond bore 102 c of the housing 102 is shown as being parallel to thefirst bore 102 a, the second bore 102 c may be perpendicular to thefirst bore 102 a or at some other angle relative to the first bore 102a.

Slidably received within the first axially extending bore 102 a is afirst piston 103. The first piston 103 has a body with a first end 103a, a second end 103 c, and a hollow interior 103 b. Present within thehollow interior 103 b of the first piston 103 is a first piston spring104. The first piston spring 104 has a first end 104 a in contact withthe interior 103 b of the first piston 103 or a volume reducer 105 and asecond end 104 b in contact with a bottom 102 b of the first axiallyextending bore 102 a of the housing 102. A first pressure chamber 111 isformed between the first piston 103 and the first axially extending bore102 a. Fluid is supplied to the first pressure chamber through a firstsupply 106 through an inlet check valve 108. The first piston 103 isbiased outwards from the housing 102 to bias the chain through the firstend 103 a of the first piston 103 by the force of the first pistonspring 104 and the pressure of oil in the first pressure chamber 111.

Alternatively, the first piston 103 may not be hollow and the firstpiston spring 104 would contact the body of the first piston 103 and thebottom 102 b of the first axially extending bore 102 a.

The second axially extending bore 102 b slidably receives a secondpiston 200. The second piston 200 has a body with a first end 200 a, asecond end 200 c and a hollow interior 200 b. The hollow interior 200 breceives a shaft 202 a of a “Y” shaped internal piston 202. The shaft202 a of the Y-shaped internal piston 202 is connected to a body with afirst end 202 d, a second end 202 b and a hollow interior 202 c. Betweenthe second end 200 c of the second piston 200 and the first end 202 d ofthe body of the internal piston 202 d is a second piston spring 201. Thesecond piston spring 201 has a first end 201 a in contact with thesecond end 200 c of the second piston 200 and a second end 201 b incontact with the first end 202 d of the internal piston 202. The secondpiston spring 201 biases the second piston 200 outwards from the housing102.

Alternatively, the second piston spring may be present between the shaft202 a of the Y-shaped internal piston 202 and the hollow interior 200 bof the second piston 200.

Within the hollow interior 202 c of the internal piston 202 is aninternal piston spring 204. The internal piston spring 204 has a firstend 204 a in contact a hollow interior 202 c of the internal piston 202or a volume reducer 206 and a second end 204 b in contact with thebottom 102 d of the second axially extending bore 102 c. The internalpiston spring 204 biases the internal piston 202 outwards from thehousing 102, biasing the second piston 200 outwards from the housing bychanging the preload on the second piston spring 201. In other words,moving the second end 201 b of the second piston spring 201 outwardsfrom the housing 102.

A second high pressure chamber 205 is formed between the hollow interior202 c of the internal piston 202 and the bottom 102 d of the secondaxially extending bore 102 c of the housing 102. Fluid is supplied tothe second pressure chamber 205 through an inlet supply 109 andpreferably a check valve 107. The inlet line 109 may or may not beconnected to the inlet supply line 106.

The second piston spring 201 has a greater spring rate or springconstant than the first piston spring 104 and the internal piston spring204.

Since there are two pistons 200, 103 to tension the chain span or belt,the leakage of the first pressure chamber 111 can be increased (asopposed to a conventional hydraulic tensioner where a certain meanpressure must be maintained within the pressure chamber to control thechain) to provide additional damping. The mean force required for chaincontrol is supplied by the second piston 200 in the second axiallyextending bore 102 c.

When the tensioner is tensioning a new chain as shown in FIG. 4a ,during operation, fluid is supplied to the first pressure chamber 111from the first inlet supply 106 and through an inlet check valve 108 andbiases the first piston 103 outwards from the housing 102 in addition tothe spring force of the first piston spring 104, biasing a span of theclosed loop chain 400 or belt as shown in FIG. 7. At the same time, thesecond piston 200 is also biased outwards from the second axiallyextending bore 102 c by the second piston spring 201 to bias a span ofthe closed loop chain or belt. Ideally, the first piston 103 and thesecond piston 200 are biased outwards from the housing 102 approximatelythe same amount. In other words, the first ends 103 a, 200 a of thefirst and the second pistons 103, 200 are aligned as shown in FIGS. 4aand 7.

When the tensioner is tensioning a worn chain without high load, duringoperation, fluid is supplied to the first pressure chamber 111 throughthe first inlet supply 106 and through an inlet check valve 108 andbiases the first piston 103 outwards from the housing 102 in addition tothe spring force of the first piston spring 104, biasing a span of theclosed loop chain 400 or belt. At the same time, the second piston 200is also biased outwards further through the second piston spring 201 dueto the movement of the internal piston 202 by the internal piston spring204 to bias the span of the closed loop chain 400 or belt. As the chainwears, additional slack is present in the chain span and the firstpiston 103 and second piston 200 would need to be extended furtheroutwards from the housing 102 to bias and adequately tension the chain400.

When the tensioner is tensioning a chain during high dynamic chain load,the high dynamic load force from the chain (shown by the arrow) pushesthe first piston 103 and the second piston 200 inwards towards thehousing 102 and then outwards from the housing 102, pumping up thepressure or pressurizing the second pressure chamber 205, by drawingfluid through the inlet check valve 107 in the second bore 102 c of thehousing 102. The pressurization of the second pressure chamber 205 inthe second bore 102 c moves the internal piston 202 outwards from thehousing 102. The movement of the internal piston 202 causes the firstend 202 d of the internal piston 202 to exert an outward force on thesecond piston 200 through the second piston spring 201, opposing theinward force of the dynamic load.

Once the inward force of the dynamic load has been opposed, fluid withinthe second pressure chamber 205 leaks to the engine through the secondaxially extending bore 102 c or through the volume reducer 206. Thisleakage reduces the mean pressure present within the second pressurechamber 205.

It should be noted that at all operating conditions, the pressure in thesecond pressure chamber 205 will pump up to maintain a minimum preloadin the second piston spring 201. When the force or preload in the secondpiston spring 201 gets too low, the internal piston 202 moves out fromthe housing, due to the internal piston spring 204 and pressure in thesecond pressure chamber 205 and draws more oil in through the inletcheck valve 107.

Therefore, the first piston 103 in the first axially extending bore 102a provides the dominant damping of the chain span or belt and the secondpiston 200 in the second axially extending bore 102 c provides thedominant and automatically adjusting spring force. The tensioner of thepresent invention automatically adjusts the mean tension force to keepthe chain tension as low as possible without sacrificing chain control,significantly improving drive efficiency at new chain conditions andconditions with dynamic loads.

FIGS. 5-6 show different options for simultaneously controlling thefirst piston and the second piston of the embodiments of the presentinvention. Referring to FIG. 5, the first piston 103 and the secondpiston 150 are directly attached through a linkage 310. Therefore, themovement of the first piston 103 and the second piston 150 are tied toeach other. When the first piston 103 and the second piston 150 arecoupled, the first piston spring 104 is optional. It should be notedthat while the linkage was shown with the tensioner of the thirdembodiment, it can similarly be applied to the tensioners of FIGS. 2a-2band 4a -4 b.

FIG. 6 shows an alternate configuration in which the first piston has anextension 312 with a top surface 312 a and a bottom surface 312 b. Thebottom surface 312 b of the extension 312 is pushed on by the secondpiston 150 as the second piston 150 is biased outwards from the housing102. It should be noted that while the linkage was shown with thetensioner of the third embodiment, it can similarly be applied to thetensioners of FIGS. 2a-2b and 4a-4b . In this embodiment, the firstpiston spring 104 is optional.

The volume reducers shown in any of the above embodiments may bereplaced with a pressure relief valve or vent.

It should also be noted that the tensioner of FIGS. 2a-2b is shown inFIG. 7, however any of the tensioners present in the application wouldwork with the chain span.

In any of the above embodiments, the external first pistons and secondpistons may have grooves on an outer circumference that engage andratchet with a pawl or ratchet clip as known in the art.

Accordingly, it is to be understood that the embodiments of theinvention herein described are merely illustrative of the application ofthe principles of the invention. Reference herein to details of theillustrated embodiments is not intended to limit the scope of theclaims, which themselves recite those features regarded as essential tothe invention.

1. A tensioner for a passive tensioner system tensioning a span of chainor a belt, comprising: a housing having a first axially extending borewith a first fluid input, and a second axially extending bore with asecond fluid input; a first piston slidably received by the firstaxially extending bore, the first piston comprising a body having afirst end and a second end; a first pressure chamber for biasing thefirst piston outwards from the housing, defined between the first pistonand the first axially extending bore and in fluid communication with thefirst fluid input; a hollow moveable sleeve slidably received by thesecond axially extending bore, comprising a hollow body having a firstopen end and a second open end separated by an inner flange having a topsurface and a bottom surface; a second piston having a body coaxiallyarranged within the moveable sleeve and received by the first open endof the movable sleeve; a second piston spring for biasing the secondpiston outwards from the moveable sleeve, received by the first open endof the moveable sleeve, having a first end contacting the second pistonand a second end contacting the top surface of a flange of the moveablesleeve; a bias spring for biasing the moveable sleeve outwards from thehousing, received within the second open end of the moveable sleeve witha first end of the bias spring in contact with the bottom surface of theinner flange of the moveable sleeve and a second end in contact with thesecond axially extending bore of the housing; a second pressure chamberdefined between the bottom surface of the inner flange of the moveablesleeve and the second bore, in fluid communication with the second fluidinput; and a check valve between the second pressure chamber and thesecond fluid input; wherein when dynamic load from the chain or beltmoves the first piston and the second piston inwards and outwards fromthe housing, fluid from the second fluid input is drawn into the secondpressure chamber through the check valve, creating a fluid pressure inthe second pressure chamber, causing the movable sleeve to move outwardsfrom the housing and exert an outward force on the second piston throughthe second piston spring, opposing an inward force of the dynamic load.2. The tensioner of claim 1, wherein the first piston and the secondpiston are coupled for movement together.
 3. The tensioner of claim 2,wherein the first piston and the second piston are coupled for movementtogether by coupling the body of the first piston and the body of thesecond piston.
 4. The tensioner of claim 2, wherein the first pistonfurther comprises an extension having a top surface and a bottomsurface, wherein the second piston pushes on the bottom surface of thefirst extension, coupling the second piston to the first piston formovement together.
 5. The tensioner of claim 1, wherein the body of thefirst piston further comprises an open end at the second end of the bodyand a closed end at the first end of the body, a bottom surface at theopen end, and a hollow interior having an inner diameter.
 6. Thetensioner of claim 5, further comprising a first piston spring forbiasing the first piston outwards from the housing, received within thehollow interior of the first piston, the first piston spring having afirst end contacting the hollow interior of the first piston and asecond end contacting the first axially extending bore.
 7. The tensionerof claim 6, wherein the second piston spring has a greater springconstant than the first piston spring and the bias spring.
 8. Thetensioner of claim 5, further comprising a volume reducer received bythe hollow interior of the first piston and the second open end of themoveable sleeve.
 9. The tensioner of claim 1, further comprising a firstpiston spring for biasing the first piston outwards from the housing,the first piston spring having a first end contacting the second end ofthe first piston and a second end contacting the first axially extendingbore.
 10. The tensioner of claim 1, wherein the first fluid input andthe second fluid input are connected to the same fluid supply.
 11. Thetensioner of claim 1, wherein the first fluid input and the second fluidinput are connected to different fluid supplies.
 12. The tensioner ofclaim 1, further comprising a check valve between the first fluid inputand the first pressure chamber.
 13. The tensioner of claim 1, furthercomprising a vent for venting fluid from the first pressure chamber. 14.The tensioner of claim 1, further comprising a vent for venting fluidfrom the second pressure chamber.
 15. The tensioner of claim 1, furthercomprising at least one pressure relief valve in the first pressurechamber. 16.-54. (canceled)